Concepts of
Green Chemistry
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37.1 Concepts of Green Chemistry (SB p.207)
Sustainable Development
United Nations 1987,
“...... Meeting the needs of the present
without compromising the ability of future
generations to meet their own needs.”
http://en.wikipedia.org/wiki/Sustainable_development
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37.1 Concepts of Green Chemistry (SB p.207)
Sustainable Development
1. Economic sustainability
2. Social sustainability
3. Environmental sustainability

Closely related to Green Chemistry
3
37.1 Concepts of Green Chemistry (SB p.208)
Green Chemistry
http://en.wikipedia.org/wiki/Green_chemistry
• During the early 1990s,
 the US Environmental Protection Agency
(EPA) coined the phrase “green chemistry”
 promote innovative chemical technologies
 reduce or eliminate the use or generation
of hazardous substances in the design,
manufacture and use of chemical products
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37.1 Concepts of Green Chemistry (SB p.208)
Green Chemistry
http://en.wikipedia.org/wiki/Green_chemistry
Green chemistry is about the design of chemical
products and processes that reduce or eliminate
the use and generation of hazardous substances.
Environmental chemistry is the chemistry of the
natural environment, and of pollutant chemicals in
nature.
Green chemistry seeks to reduce and prevent
pollution at its source.
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Green Chemistry can also be described as
1. Sustainable chemistry
2. Chemistry that is benign by design
3. Pollution prevention at the molecular level
4. All of the above
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Green chemistry can be regarded as a
reduction process.
It aims at reducing the cost, waste, materials,
energy, risk and hazard.
Waste
Materials
Cost
Reducing
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Risk and
hazard
Energy
The Twelve Principles of Green Chemistry:
1. Waste Prevention
2. Maximizing Atom Economy
3. Using Less Hazardous Chemical Syntheses
4. Producing Safer Chemical Products
5. Using Safer Solvents and Auxiliaries
6. Designing for Energy Efficiency
7. Using Renewable Raw Materials
8. Reducing Derivatives (fewer steps)
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The Twelve Principles of Green Chemistry:
9. Using Catalysts
10. Designing Degradable Chemical Products
11. Developing Real-time Analysis for Pollution
Prevention
12. Minimizing the Potential for Chemical
Accidents
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1. Waste prevention
It is better to prevent the formation of
waste than to treat or clean up the waste.
Chemical wastes are undesirable products
from chemical reactions. They are usually
hazardous to the environment.
Industrial processes should be designed
to minimize the generation of waste.
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2. Maximizing atom economy
Traditionally, the success of a chemical
reaction is judged by the percentage
yield of product.
It is possible to achieve 100% yield but
the reaction may generate waste that is
far greater in mass and volume than that
of the desired product.
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Consider the following reaction:
AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)
~100%
yield
undesirable
Suggest reactions that have no undesirable
products.
Na(s) + Cl2(g)  2NaCl(s)
Direct
combination
N2(g) + 3H2(g)  2NH3(s)
Addition
CH2=CH2(g) + H2(g)  C2H6(g)
reaction
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Concept of atom economy
Atom economy
Mass ofdesired product

 100%
Total mass of all products (or reactants)
The greater the value of the atom
economy, the better is the reaction to
convert all the reactant atoms to the
desired product.  Less waste
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Calculate the atom economy of each of the
following conversions
SN1  side products
C4H9OH + KBr + H2SO4  C4H9Br + KHSO4 + H2O
136.9
AE 
136.9
 100%
136.9  136.2  18.0
AE 
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3  136.9
 100%
3  136.9  82.0
18.0
= 47.0%
3C4H9OH + PBr3  3C4H9Br + H3PO3
3136.9
136.2
Non-SN
82.0
= 83.4%
Greener
H3C
H3C
C
CH 2
+ 2HOCl + Ca(OH)2
C
2
CH2
H
O
H
258.0
AE 
2  58.0
 100%
2  58.0  111.0  2  18.0
H3C
C
CH 2
+ H2O2
catalyst
H3C
C
CH 2
O
58.0
58.0
AE 
 100%
58.0  18.0
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111.0 218.0
= 44.1%
H
H
+ CaCl2 + 2H2O
= 76.3%
+ H2O
18.0
H3C
H3C
C
CH 2
H
+ 2HOCl + Ca(OH)2
C
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CH 2
+ H2O2
catalyst
Less
harmful
CH2
H
O
More
harmful
H3C
H
C
2
258.0
+ CaCl2 + 2H2O
111.0 218.0
harmless
H3C
C
CH 2
H
O
58.0
+ H2O
18.0
Greener
3. Using less hazardous chemical
syntheses
Chemical syntheses should be designed to
use or generate substances that possess
little or no toxicity to humans and the
environment.
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Consider the synthesis of adipic acid
(HOOC(CH2)4COOH).
Adipic acid is the essential feedstock
for making synthetic fibres such as
nylon.
Traditional method
C6H6
HOOC(CH2)4COOH
New method
C6H12O6
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HOOC(CH2)4COOH
Traditional Method
(1) H2, Ni-Al2O3, 2555 atm
benzene
cyclohexane
(2) Co/O2, 89.5 atm
cyclohexanone
cyclohexanol
(3) conc. HNO3
adipic acid
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dinitrogen
oxide
Traditional Method
(1) H2, Ni-Al2O3, 2555 atm
benzene
cyclohexane
The
synthesis has the following risks
(2) Co/O2, 89.5 atm
and hazards:
•
cyclohexanone
cyclohexanol
In step 1, the starting material for the
synthesis is benzene, which is a known
(3) conc. HNO3
carcinogen.
dinitrogen
adipic acid
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oxide
•
Traditional Method
In(1)step
2,2Othe
oxidation of cyclohexane
H2, Ni-Al
3, 2555 atm
with air may lead to an uncontrolled
benzene
cyclohexane
reaction. It has the
risk of explosion.
(2) Co/O2, 89.5 atm
•
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cyclohexanone
cyclohexanol
Not all of the cobalt catalysts can be
(3) conc. HNO3 This may lead to the disposal
recovered.
dinitrogen
of a heavy metal to theadipic
environment.
acid
oxide
Traditional Method
•
(1) H2, Ni-Al2O3, 2555 atm
In step 3, dinitrogen oxide or nitrous
benzene
cyclohexane
oxide (N2O) gas is
produced as a byproduct. It is a greenhouse gas with an
effect
which is 200 times the effect of
(2) Co/O2, 89.5 atm
carbon dioxide.
cyclohexanone
cyclohexanol
(3) conc. HNO3
adipic acid
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dinitrogen
oxide
biosynthetic pathway
1
2
3
(1) E. coli
D-glucose
shikimic acid
(2) E. coli
3-dehydroshikimic acid
muconic acid
Much greener
(3) Pt/H2, 34 atm
adipic acid
1. the starting material, glucose, is harmless.
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biosynthetic pathway
(1) E. coli
D-glucose
(2) E. coli
3-dehydroshikimic acid
muconic acid
Much greener
(3) Pt/H2, 34 atm
adipic acid
2. E. coli is used to catalyse two steps of the
reaction. This reduces the use of certain
chemical reagents with significant toxicity.
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biosynthetic pathway
(1) E. coli
D-glucose
(2) E. coli
3-dehydroshikimic acid
muconic acid
Much greener
(3) Pt/H2, 34 atm
adipic acid
3. there are no by-products generated during
the synthesis.
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4. Producing safer chemical
products
The chemical products synthesized
should be safe to use.
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For example, chemicals called organotin
compounds(Anti-biofouling agent) were
used in large ships to prevent
accumulation of barnacles(藤壺) and
marine plants traditionally.
The accumulation of barnacles(藤壺)on the ship
may
increase
the
resistance
to
its
movement.
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However, organotin compounds are highly
toxic to the surrounding marine life.
Then, Rohm and Haas Company developed
a non-toxic alternative called Sea-NineTM.
It degrades quickly in the marine
environment and is not toxic to the
surrounding marine life.
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5. Using safer solvents and
auxiliaries
The solvents and auxiliaries (e.g.
drying agent, blowing agent, etc.) used
in chemical syntheses will become part
of the wastes.
They may cause environmental pollution
and health hazard.
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CFCs : unreactive
volatile liquids or easily liquefied gases
low flammability
low toxicity
 Cleaning solvents
Propellants
Refrigerants
Blowing agents
They were eventually banned because
they deplete the ozone layer.
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Screening of UV radiations by ozone
layer
=215-295 nm
2O3
=250 nm
3O2
~99% of UV radiation from the sun are
screened out
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They were eventually banned because of
their ability to deplete the ozone layer.
uv
CFCl3 → CFCl2 + Cl
Cl + O3 → ClO + O2
ClO + O3 → Cl + 2O2
chain
reaction
One Cl free radical can destroy 100000
ozone molecules
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Nowadays, CO2 is used to replace CFCs as the
blowing agent.
CO2 is non-toxic and non-flammable. It does
not deplete the ozone layer.
STYROFOAM
produced with carbon
dioxide as the blowing
agent
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Many solvents currently used in the chemical
industry are harmful and volatile
They are known as
Volatile Organic Compounds (VOCs)
E.g. Propanone, benzene,
dichloromethane, dibromomethane,
chloroform and carbon tetrachloride.
VOCs + NOx
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UV
photochemical smog
1. Using ionic liquids as solvents
E.g.
N
N
BF4
Low m.p. due to poor packing between ions of
significantly different sizes
High b.p. due to ionic nature
 Low volatility
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N
N
BF4
N
N
BF4
More viscous
By modifying the structures and charges of the ions,
ionic liquids can exhibit specific properties such as
m.p., viscosity, volatility & hydrophobicity to meet the
particular needs of a synthesis.
Designer solvents
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A “Greener” Route to Adipic Acid.
Sato, K.; Aoki, M.; Noyori, R.
Science, 1998
Na2WO4 as catalyst
146.0
COOH
+ 4H2O
+ 4H2O2
[CH3(n-C8H17)3N]HSO4
30%
as phase transfer agent
75-90C, 8h
418.0
COOH
93% yield
The reaction can be carried out in aqueous medium
146.0
 100% = 67.0%
Atom economy =
146.0  4  18.0
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Advantages of using ionic liquids over using VOCs
as solvents (2010 AL Paper 1 Q.6)
1. Tailor-made
2. Low b.p.
Not easily escape to the environment
Volatile organic reactants/products can be
easily removed by simple distillation.
The solvents can be easily recycled and reused
3. Low flammability due to their low vapour
pressure
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Advantages of using ionic liquids over using VOCs
as solvents
4. Wide liquid range due to low m.p. and high b.p.
Organic syntheses can occur at higher
temperatures
5. Ionic nature can allow organic syntheses
involving ionic species.
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2. Using supercritical CO2 as solvent in
decaffeination
Coffee beans
with
caffeine
decaffenation
Coffee beans
without
caffeine
In the past, solvents used for decaffeination are
harmful to the environment and human beings
E.g. CHCl3, CH2Cl2, benzene
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CO2
As dense as a liquid
As mobile as a gas
Supercritical
fluid
B
P / atm
C
Pc= 73atm
Liquid
Solid
Gas
T
Vapour
A
Tc= 31C
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T / C
CO2
Decaffeination using
supercritical CO2
Supercritical
fluid
B
P / atm
C
Pc= 73atm
Liquid
Solid
Gas
T
Vapour
A
Tc= 31C
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T / C